The $\beta$-delayed neutron emission of ${}^{83,84}\mathrm{Ga}$ isotopes was studied using the neutron time-of-flight technique. The measured neutron energy spectra showed emission from states at excitation energies high above the neutron separation energy and previously not observed in the $\beta$ decay of midmass nuclei. The large decay strength deduced from the observed intense neutron emission is a signature of Gamow-Teller transformation. This observation was interpreted as evidence for allowed $\beta$ decay to ${}^{78}\mathrm{Ni}$ core-excited states in ${}^{83,84}\mathrm{Ge}$ favored by shell effects. We developed shell model calculations in the proton $fp{g}_{9/2}$ and neutron extended $fp{g}_{9/2}+d_{5/2}$ valence space using realistic interactions that were used to understand measured $\beta$-decay lifetimes. We conclude that enhanced, concentrated $\beta$-decay strength for neutron-unbound states may be common for very neutron-rich nuclei. This leads to intense $\beta$-delayed high-energy neutron and strong multineutron emission probabilities that in turn affect astrophysical nucleosynthesis models.

We report total absorption spectroscopy measurements of ${}^{92}\mathrm{Rb}$, ${}^{96\mathrm{gs}}\mathrm{Y}$, and ${}^{142}\mathrm{Cs}$ $\beta$ decays, which are the most important contributors to the high energy ${\overline{\nu }}_e$ spectral shape in nuclear reactors. These three $\beta$ decays contribute 43% of the ${\overline{\nu }}_e$ flux near 5.5 MeV emitted by nuclear reactors. This ${\overline{\nu }}_e$ energy is particularly interesting due to spectral features recently observed in several experiments including the Daya Bay, Double Chooz, and RENO Collaborations. Measurements were conducted at Oak Ridge National Laboratory by means of proton-induced fission of ${}^{238}\mathrm{U}$ with on-line mass separation of fission fragments and the Modular Total Absorption Spectrometer. We observe a $\beta$-decay pattern that is similar to recent measurements of ${}^{92}\mathrm{Rb}$, with a ground-state to ground-state $\beta$ feeding of 91(3)%. We verify the ${}^{96\mathrm{gs}}\mathrm{Y}$ ground-state to ground-state $\beta$ feeding of 95.5(20)%. Our measurements substantially modify the $\beta$-decay feedings of ${}^{142}\mathrm{Cs}$, reducing the $\beta$ feeding to ${}^{142}\mathrm{Ba}$ states below 2 MeV by 32% when compared with the latest evaluations. Our results increase the discrepancy between the observed and the expected reactor ${\overline{\nu }}_e$ flux between 5 and 7 MeV, the maximum excess increases from $\sim 10\%$ to $\sim 12\%$.

The longitudinal and transverse electromagnetic response functions of ${}^{12}\mathrm{C}$ are computed in a “first-principles” Green’s function Monte Carlo calculation, based on realistic two- and three-nucleon interactions and associated one- and two-body currents. We find excellent agreement between theory and experiment and, in particular, no evidence for the quenching of the measured versus calculated longitudinal response. This is further corroborated by a reanalysis of the Coulomb sum rule, in which the contributions from the low-lying $J^{\pi }=2^{+}$, $0_2^{+}$ (Hoyle), and $4^{+}$ states in ${}^{12}\mathrm{C}$ are accounted for explicitly in evaluating the total inelastic strength.

One-neutron knockout reactions have been performed on a beam of radioactive ${}^{53}\mathrm{Co}$ in a high-spin isomeric state. The analysis is shown to yield a highly selective population of high-spin states in an exotic nucleus with a significant cross section, and hence represents a technique that is applicable to the planned new generation of fragmentation-based radioactive beam facilities. Additionally, the relative cross sections among the excited states can be predicted to a high level of accuracy when reliable shell-model input is available. The work has resulted in a new level scheme, up to the $11^{+}$ band-termination state, of the proton-rich nucleus ${}^{52}\mathrm{Co}$ ($Z=27$, $N=25$). This has in turn enabled a study of mirror energy differences in the $A=52$ odd-odd mirror nuclei, interpreted in terms of isospin-nonconserving (INC) forces in nuclei. The analysis demonstrates the importance of using a full set of $J$-dependent INC terms to explain the experimental observations.

Local Lorentz invariance violating (LLIV) and Einstein equivalence principle violating (EEPV) effects in atomic experiments are discussed. The EEPV effects are strongly enhanced in the narrow 7.8 eV transition in the ${}_{90}{}^{229}\mathrm{Th}$ nucleus. The nuclear LLIV tensors describing the anisotropy in the maximal attainable speed for massive particles (analog of the Michelson-Morley experiment for light) are expressed in terms of the experimental values of the nuclear quadrupole moments. Calculations for nuclei of experimental interest ${}_{55}{}^{133}\mathrm{Cs}$, ${}_{37}{}^{85}\mathrm{Rb}$, ${}_{37}{}^{87}\mathrm{Rb}$, ${}_{80}{}^{201}\mathrm{Hg}$, ${}_{54}{}^{131}\mathrm{Xe}$, and ${}_{10}{}^{21}\mathrm{Ne}$ are performed. The results for ${}_{10}{}^{21}\mathrm{Ne}$ are used to improve the limits on the proton LLIV interaction constants by 4 orders of magnitude.

Shape parameters of a weakly deformed ground-state band and highly deformed slightly triaxial sideband in ${}^{42}\mathrm{Ca}$ were determined from $E2$ matrix elements measured in the first low-energy Coulomb excitation experiment performed with AGATA. The picture of two coexisting structures is well reproduced by new state-of-the-art large-scale shell model and beyond-mean-field calculations. Experimental evidence for superdeformation of the band built on $0_2^{+}$ has been obtained and the role of triaxiality in the $A\sim 40$ mass region is discussed. Furthermore, the potential of Coulomb excitation as a tool to study superdeformation has been demonstrated for the first time.

Resonance plays critical roles in the formation of many physical phenomena, and several methods have been developed for the exploration of resonance. In this work, we propose a new scheme for resonance by solving the Dirac equation in the complex momentum representation, in which the resonant states are exposed clearly in the complex momentum plane and the resonance parameters can be determined precisely without imposing unphysical parameters. Combined with the relativistic mean-field theory, this method is applied to probe the resonances in ${}^{120}\mathrm{Sn}$ with the energies, widths, and wave functions being obtained. Compared to other methods, this method is not only very effective for narrow resonances, but also can be reliably applied to broad resonances.

We use a top-down holographic model for strongly interacting quark matter to study the properties of neutron stars. When the corresponding equation of state (EOS) is matched with state-of-the-art results for dense nuclear matter, we consistently observe a first-order phase transition at densities between 2 and 7 times the nuclear saturation density. Solving the Tolman-Oppenheimer-Volkov equations with the resulting hybrid EOSs, we find maximal stellar masses in excess of two solar masses, albeit somewhat smaller than those obtained with simple extrapolations of the nuclear matter EOSs. Our calculation predicts that no quark matter exists inside neutron stars.

The $\beta$-delayed neutron emission probabilities of neutron rich Hg and Tl nuclei have been measured together with $\beta$-decay half-lives for 20 isotopes of Au, Hg, Tl, Pb, and Bi in the mass region $N\gtrsim 126$. These are the heaviest species where neutron emission has been observed so far. These measurements provide key information to evaluate the performance of nuclear microscopic and phenomenological models in reproducing the high-energy part of the $\beta$-decay strength distribution. This provides important constraints on global theoretical models currently used in $r$-process nucleosynthesis.

High $p_T>10\mathrm{GeV}$ elliptic flow, which is experimentally measured via the correlation between soft and hard hadrons, receives competing contributions from event-by-event fluctuations of the low-$p_T$ elliptic flow and event-plane angle fluctuations in the soft sector. In this Letter, a proper account of these event-by-event fluctuations in the soft sector, modeled via viscous hydrodynamics, is combined with a jet-energy-loss model to reveal that the positive contribution from low-$p_T$ $v_2$ fluctuations overwhelms the negative contributions from event-plane fluctuations. This leads to an enhancement of high-$p_T>10\mathrm{GeV}$ elliptic flow in comparison to previous calculations and provides a natural solution to the decade-long high-$p_T$ $R_{AA}\otimes v_2$ puzzle. We also present the first theoretical calculation of high-$p_T$ $v_3$, which is shown to be compatible with current LHC data. Furthermore, we discuss how short-wavelength jet-medium physics can be deconvoluted from the physics of soft, bulk event-by-event flow observables using event-shape engineering techniques.

The pseudorapidity density of charged particles, $d{N}_{\mathrm{ch}}/d\eta$, at midrapidity in Pb-Pb collisions has been measured at a center-of-mass energy per nucleon pair of $\sqrt{s_{NN}}=5.02\mathrm{TeV}$. For the 5% most central collisions, we measure a value of $1943\pm 54$. The rise in $d{N}_{\mathrm{ch}}/d\eta$ as a function of $\sqrt{s_{NN}}$ is steeper than that observed in proton-proton collisions and follows the trend established by measurements at lower energy. The increase of $d{N}_{\mathrm{ch}}/d\eta$ as a function of the average number of participant nucleons, $⟨N_{\text{part}}⟩$, calculated in a Glauber model, is compared with the previous measurement at $\sqrt{s_{NN}}=2.76\mathrm{TeV}$. A constant factor of about 1.2 describes the increase in $d{N}_{\mathrm{ch}}/d\eta$ from $\sqrt{s_{NN}}=2.76$ to 5.02 TeV for all centrality classes, within the measured range of 0%–80% centrality. The results are also compared to models based on different mechanisms for particle production in nuclear collisions.

We report on the first measurement of an excess in the yield of $J/\psi$ at very low transverse momentum ($p_T<0.3\mathrm{GeV}/c$) in peripheral hadronic Pb-Pb collisions at $\sqrt{s_{\mathrm{NN}}}=2.76\mathrm{TeV}$, performed by ALICE at the CERN LHC. Remarkably, the measured nuclear modification factor of $J/\psi$ in the rapidity range $2.5<y<4$ reaches about 7 (2) in the $p_T$ range $0–0.3\mathrm{GeV}/c$ in the 70%–90% (50%–70%) centrality class. The $J/\psi$ production cross section associated with the observed excess is obtained under the hypothesis that coherent photoproduction of $J/\psi$ is the underlying physics mechanism. If confirmed, the observation of $J/\psi$ coherent photoproduction in Pb-Pb collisions at impact parameters smaller than twice the nuclear radius opens new theoretical and experimental challenges and opportunities. In particular, coherent photoproduction accompanying hadronic collisions may provide insight into the dynamics of photoproduction and nuclear reactions, as well as become a novel probe of the quark-gluon plasma.

We demonstrate that measurements of rapidity differential anisotropic flow in heavy-ion collisions can constrain the temperature dependence of the shear viscosity to entropy density ratio $\eta /s$ of QCD matter. Comparing results from hydrodynamic calculations with experimental data from the RHIC, we find evidence for a small $\eta /s\approx 0.04$ in the QCD crossover region and a strong temperature dependence in the hadronic phase. A temperature independent $\eta /s$ is disfavored by the data. We further show that measurements of the event-by-event flow as a function of rapidity can be used to independently constrain the initial state fluctuations in three dimensions and the temperature dependent transport properties of QCD matter.

The strong dependence of Coulomb energies on nuclear radii makes it possible to extract the latter from calculations of the former. The resulting estimates of neutron skins indicate that two mechanisms are involved. The first one—isovector monopole polarizability—amounts to noting that when a particle is added to a system it drives the radii of neutrons and protons in different directions, tending to equalize the radii of both fluids independently of the neutron excess. This mechanism is well understood and the Duflo-Zuker (small) neutron skin values derived 14 years ago are consistent with recent measures and estimates. The alternative mechanism involves halo orbits whose huge sizes tend to make the neutron skins larger and have a subtle influence on the radial behavior of $sd$ and $pf$ shell nuclei. In particular, they account for the sudden rise in the isotope shifts of nuclei beyond $N=28$ and the near constancy of radii in the $A=40–56$ region. This mechanism, detected here for the first time, is not well understood and may well go beyond the Efimov physics usually associated with halo orbits.